Department of Pharmacology and Molecular Sciences, Johns Hopkins University School of Medicine 725 North Wolfe Street Baltimore, MD 21205, USA.
Medicine Design, Pfizer, Groton, CT 06340, USA.
Nucleic Acids Res. 2023 Dec 11;51(22):12443-12458. doi: 10.1093/nar/gkad971.
The dNTPase activity of tetrameric SAM and HD domain containing deoxynucleoside triphosphate triphosphohydrolase 1 (SAMHD1) plays a critical role in cellular dNTP regulation. SAMHD1 also associates with stalled DNA replication forks, DNA repair foci, ssRNA and telomeres. The above functions require nucleic acid binding by SAMHD1, which may be modulated by its oligomeric state. Here we establish in cryo-EM and biochemical studies that the guanine-specific A1 activator site of each SAMHD1 monomer is used to target the enzyme to guanine nucleotides within single-stranded (ss) DNA and RNA. Remarkably, nucleic acid strands containing a single guanine base induce dimeric SAMHD1, while two or more guanines with ∼20 nucleotide spacing induce a tetrameric form. A cryo-EM structure of ssRNA-bound tetrameric SAMHD1 shows how ssRNA strands bridge two SAMHD1 dimers and stabilize the structure. This ssRNA-bound tetramer is inactive with respect to dNTPase and RNase activity.
四聚体 SAM 和 HD 结构域包含的脱氧核苷三磷酸三磷酸水解酶 1（SAMHD1）的 dNTPase 活性在细胞内 dNTP 调节中起着关键作用。SAMHD1 还与停滞的 DNA 复制叉、DNA 修复焦点、ssRNA 和端粒相关联。上述功能需要 SAMHD1 与核酸结合，其寡聚状态可能会受到调节。在这里，我们通过冷冻电镜和生化研究证实，每个 SAMHD1 单体的鸟嘌呤特异性 A1 激活位点被用于将酶靶向单链（ss）DNA 和 RNA 中的鸟嘌呤核苷酸。值得注意的是，含有单个鸟嘌呤碱基的核酸链诱导二聚体 SAMHD1，而具有约 20 个核苷酸间隔的两个或更多鸟嘌呤则诱导四聚体形式。ssRNA 结合的四聚体 SAMHD1 的冷冻电镜结构显示了 ssRNA 链如何桥接两个 SAMHD1 二聚体并稳定结构。这种 ssRNA 结合的四聚体在 dNTPase 和 RNase 活性方面是无活性的。
